With repairs complete, Nuclear Regulatory Commission spokesman Neil Sheehan said that plant workers are slowly bringing the reactor back up to full power. As of early Dec. 30 it was at 1 percent power, Sheehan said.

Two NRC inspectors are on hand to monitor the startup, as was also the case with the repair work. Sheehan said the inspectors did not identify any concerns with the repairs and that the work went well. Pilgrim's owner, Entergy Corp., will send the broken valve to a vendor for analysis.

Pilgrim is in its 39th year of operation and is presently seeking a 20-year license extension from the NRC — an effort that has been questioned by some Massachusetts officials and activists. It's not known when the NRC will make a ruling on that application. The reactor contributes 677 megawatts to the New England energy grid, enough to power nearly 700,000 homes.